Name: __________________________________________________________Date:__________________Period:________
Molecular Geometry
Introduction
As with many of the properties, molecular shape can be determined by electronic structure of the bonded atoms. Predictions
regarding the shape of the molecule can be made using valence-shell electron-pair repulsion (VSEPR) theory. In VSEPR theory electrons
within bonds or lone pair electrons can be thought of as “electron clouds”. These negatively charged clouds will repel one another and
stay as far apart from one another as possible, thus resulting in a specific shape.
It is important to note, that when determining electron clouds a single bond is counted the same way as a double or triple bond. For
example, a single bond is counted as one electron cloud. The same is true for a double or triple bond; they are counted as one electron
cloud.
For this lab activity you will investigate the different molecular shapes by drawing Lewis structures and comparing those structures to
computer models using Models 360. Models 360 is a collection of interactive 3-D models that you can manipulate to investigate bonding
and molecular geometry.
Prelab
Part 1
Determine the Lewis structures for all of the compounds listed in Table 1. The following outlines the procedure for writing Lewis
structures:
Part 2
Now that you have determined the Lewis structures for each of the chemical formulas, use Models 360 to confirm your Lewis
structure. To access Models 360 go to www.chemeddl.org. Click on Models 360 to open the program. To find the Lewis structures for
your molecules search each formula using the “Find:” box in the upper right hand corner of the screen. In the box you will find the default
“Name/Formula”. Type the formula in that box. A drop down menu will appear. Choose the name and formula that match your formula
and a 3-D molecular representation will appear in the black window. (The name and formula will appear above the window. Please check
this to make sure you have the right molecule).
To confirm your Lewis structure, open the images tab located directly under the Models 360 heading. The images tab will be yellow
and when activated will become blue. Under this tab you will see the correct Lewis structure for the molecule. Compare this Lewis
structure with the Lewis structure that you created. Remember, the orientation of the bonds and lone pair electrons around the central
atoms doesn’t matter. For example, it doesn’t matter that the lone pair electrons on your Lewis structure are on the right and the Models
360 structure show them on the left. What does matter is the number of bonded atoms (and how they are bonded (single, double, or
triple bonds) and the number of lone pair electrons.
If you find any differences between your Lewis structure and the Models 360 structure make note of what error you made in your
prelab and correct your drawing.
Once you have finished checking your Lewis structures, click on the “3D Structure: Jmol” tab and take some time to familiarize
yourself with Models 360. Explore some of the features that are found to the right of the black window. We will explore some of the
options during the lab.
Molecular Geometry Prelab
Prelab questions:
1) Discuss any errors you may have made in determining Lewis structures and what you learned from them. 
2) What are your first impressions of Lewis structures and Models 360? Likes/dislikes or questions.
Laboratory Procedure
Part 1 – Determining Geometries from 3-D Representations
For this lab you will build 3-D molecular models using the Models 360. One of the goals for this lab is to help you develop
mental representations of what the shapes of molecules look like in 3-D. Each of you will have different needs when it comes
to meeting this goal, so take advantage of whatever resource works best for you.
In the prelab you determined the Lewis structures for each of the compounds. Now we will look at 3-D representations of
each molecule. Using Models 360 build 3-D representations for each molecule. Use the same procedure that you used in the
prelab to search for you molecules in Models 360.
Instead of drawing out each ball-stick model you’ll take a picture and paste it into Table 1. To do this, click on “Take a
Picture” underneath the image. A separate window will pop-up, press on the photo and choose copy. Open up Table1 within
Notability. Choose text and paste the image within the appropriate box.
Part 2 – Bond Angles
Using the information you learned on Bond Angles, predict the calculated bond angles for each of your molecules. Using
Models 360 check your bond angles for each of the molecules in Table 1. To do this, make sure the “3-D structure: Jmol” tab is
open. On the right side of 3-D representation you will see a dropdown menu labeled “Display”. Under this menu you will see
a box labeled “Bond Angles”. Click on that box to display the bond angles and record these values in Table 1.
Part 3 – Polarity
One way to visualize the uneven distribution of the electrons is to represent the molecule using an electrostatic potential
map. Based on the steps you learned yesterday, predict with each molecule will be polar or non-polar. Models 360 will
represent the calculated distribution of the electrons is displayed using color. The blue region represents an area of electron
deficiency (partial positive charge) and the red region represents an area of electron surplus (partial negative charge). These
partial charges are represented by the Greek letter delta (δ+ or δ-). Remember, this is not a full transfer of electrons, but an
uneven distribution of electrons.
Below is the electrostatic potential plot for water (H2O):
Notice that the region around the oxygen atom is red in color representing an area of
electron surplus (partial negative charge) and the region around the hydrogen atoms are
blue representing an area of electron deficiency (partial positive charge). Due to this
separation of charge, a region that is positive and a region that is negative, we would say
this molecule has a dipole moment or is a polar molecule. The molecular dipole is often
represented using an arrow with a cross at the end indicating the direction of the dipole.
The arrow points in the direction of the negative end as shown below:
In contrast to water, tetrachloromethane (CCl4) is shown below:
Notice that there is not a positive (blue) or negative region (red) within this molecule.
Tetrachloromethane is therefore classified as a nonpolar molecule.
To view the electrostatic potential maps for your molecules, open Models 360. Click on
the “Molecular Elecrostatic Potential (MEP)” drop down menu to the right. Then click on
“MEP on van der Waals Surface”. To show the molecular dipole, click on the box next to
“Molecular Dipole”
We are going to insert the Electrostatic Map into Table 1 to do this you’ll take a picture
and paste it into Table 1. Click on “Take a Picture” underneath the image. A separate window
will pop-up, press on the photo and choose copy. Open up Table1 within Notability. Choose
text and paste the image within the appropriate box.
δ+
δ-
Part 4
For this part of the activity you will select examples of some of the different geometries and present them add them into
Table 1. You will need to find representations of linear, trigonal planar, tetrahedral, trigonal pyramidal, and bent molecules.
To find these molecules go to Models 360 and open the advanced search option found in the upper right hand corner. On
the left hand side you will see a list of drop down menus. Select the menu titled “VSEPR shape”. This will give you a list of
molecular geometries to choose. Choose one by clicking on “Find Selected” located above the drop down menu. A list of
molecules will be viewed to the right. Choose one of the molecules and select “View Molecule”. This will open the molecule in
the Jmol 3D structure.
Complete the table 1 for Part 4 by cutting and pasting the images from Models360.
Table 1 – Parts 1, 2, & 3
Chemical formula
Lewis structure
Molecular shape
NH3
AlCl3
Polarity
105.8º
Trigonal pyramidal
CO2
Bond angles
Polar
Chemical formula
H3O+
03
H2S
Lewis structure
Molecular shape
Bond angles
Polarity
Chemical formula
ClF3
SF4
PCl5
Lewis structure
Molecular shape
Bond angles
Polarity
Chemical formula
BrF5
SF6
CH4
Lewis structure
Molecular shape
Bond angles
Polarity
Table 1 – Parts 4
Chemical formula
Lewis structure
Molecular shape
Linear
Trigonal
Planar
Tetrahedral
Bond angles
Polarity
Chemical formula
Lewis structure
Molecular shape
Trigonal
Pyramidal
Bent
Bond angles
Polarity